Dominant Trap Research Articles

A numerical feasibility study of CO2 foam for carbon utilization and storage in a depleted, high salinity, carbonate oil reservoir

Carbon Capture, Utilization, and Storage (CCUS) offers a viable solution to reduce the carbon footprint in the petroleum industry, and foam injection presents a promising method to achieve this while simultaneously increasing oil recovery. In this work, we studied the feasibility of CO2 foam for co-optimizing enhanced oil recovery and CO2 storage in a high-salinity carbonate formation. The simulated hydrodynamic model is a depleted formation containing 30% residual oil, with three mechanisms for CO2 storage: solubility, residual, and mineralization trapping mechanisms. The results showed that after 20 years, oil recovery during foam injection was 2.7 times higher than CO2 injection, and the CO2 stored during foam flooding was 38% higher than CO2 injection. Notably, foam injection also increased CO2 storage capacity by 2.6 times, indicating the potential to store around 2 gigatons of CO2 in the simulated model. This was attributed to the ability of foam to significantly reduce gas mobility and thus form isolated bubbles through its Jamin effect. Residual trapping was the dominant trapping mechanism, contributing to over 70% of the total CO2 trapped, attributed to the reduction in the dissolution of CO2 in brine due to the high salinity of the aqueous medium. CO2 mineralization was also studied, showing the least trapping efficiency and the dissolution trend of all the carbonate minerals. This study illustrates a novel CO2 utilization and storage technique in which CO2 is concurrently sequestered while enhancing oil recovery in a depleted oil reservoir by injecting CO2 as foam. The relevance of this study lies in its potential to provide a dual benefit of reducing greenhouse gas emissions and boosting oil production, offering a sustainable approach for the petroleum industry.

Investigation of gas residuals in sandstone formations via X-ray core-flooding experiments: Implication for subsurface hydrogen storage

The production and utilization of hydrogen (H2) as a clean energy source offer a promising solution towards achieving net-zero carbon emissions. Utilizing sandstone formations for geological hydrogen storage presents a viable option for the practical implementation of the hydrogen economy, offering both safe and large-scale containment capabilities. Accurate assessment of gas displacement behavior in porous media plays a critical role in understanding gas saturation, gas residual, and long-term storage duration. However, there are limited studies available on dynamic displacements for hydrogen storage applications. This study aims to enhance the understanding of gas flow behavior in sandstone rocks for different gas types and determine the role of capillary pressure and gas wettability during hydrogen storage. A series of gas core-flooding experiments are performed on a brine-saturated sandstone core sample using three different gases (CO2, CH4, and H2). X-ray scanning technique is applied to detect the gas saturation and gas residual after the core-flooding experiments. The results indicate that the average gas saturation ranges between 25 and 40%, with zero gas residual for all gases, suggesting that the gas residuals in this clean sandstone sample are unaffected by the gas type. Initially, the capillary pressure profile for the sample displayed low brine saturation at 200 psi, indicating very low capillary pressure in the sample due to the high permeability and large pore radius, despite the strong water-wetting behavior of the sample. Moreover, the obtained results indicate the high potential for gas recovery (especially for hydrogen during withdrawal cycles), and the high displacement efficiency in sandstone rocks. The reported low gas residual suggests that the wettability of the rock is not affected by gas injection, and it appears that the wettability and capillary pressure are not the controlling factors for gas storage in this sandstone sample. This observation suggests that the structural trapping mechanism is most likely to be the dominant trapping mechanism in this shallow high permeable sandstone rock. Also, the injection of cushion gases such as CO2 and CH4 indicated similar results to hydrogen injection, due to the low capillary pressure and high permeability in this sandstone sample. The findings of this study can greatly enhance the understanding of gas injection, displacement behavior, and gas residuals in sandstone rocks related to underground hydrogen storage.

Experimental and modeling study of CO2 solubility in formation brines at in-situ conditions

The dissolution of CO2 into formation brine, one of the dominant trapping mechanisms for geological carbon storage (GCS) in deep saline aquifers, has been widely investigated. Most experimental and modeling studies focused on the CO2 solubility in synthetic brines. However, rare studies have been performed to investigate CO2 solubility in real formation brines, especially when ion-ion interactions were considered. In this work, the CO2 solubility of seventy formation brines from major basins in China including the Junggar basin, Ordos basin, and North and South Songliao basin was measured at in-situ pressure and temperature conditions. Experimental results show that CO2 solubility has a strong relationship with pressure and total dissolved solids (TDS), while the relationship between solubility and temperature is weak. Three solubility regions were classified in terms of depth. In Regions I and III, CO2 solubility increases with depth and is independent with depth in Region II. However, the effect of salinity on CO2 solubility was observed in all regions. Additionally, a modified Duan's model used for a mixed-salt system was proposed using dataset from this study and literature. Comparisons with Duan's model for CO2 solubility in mixed-salt systems show the average absolute relative deviation equals 5.14%, which reveals a clear improvement in the modified model. In addition, the validation of the model was performed, and results show that the average absolute relative deviation before and after improvement are 12.10% and 5.11%, respectively, indicating the high accuracy of the improved model. Overall, this research improves the understanding of CO2 solubility in real formation brines and illustrates the efficiency and accuracy of the modified model, which is crucial for the evaluation of the CO2 storage capacity, fate of CO2 over storage site life for commercial GCS projects.

Charge carrier transport mechanism in plasma polymerized methyl acrylate thin films

Plasma-polymerized methyl acrylate thin films (PPMA) of thicknesses 115 to 290 nm were prepared using a capacitively coupled glow discharge plasma reactor. The current density-voltage (J-V) characteristics of the Aluminum/PPMA/Aluminum sandwich configuration were studied between 0.1 and 75 V over the temperature region from 298 K to 398 K for various thicknesses of PPMA thin films. J-V curves show that the conduction current follows Ohm's law in the low voltage area, but that in the high voltage range, the behavior is attributed to be space charge-limited conduction (SCLC) in PPMA thin films. The free carrier density, the trap density and carrier mobility have been determined to be around 1.77 × 1023 to 5.86 × 1023 m−3, 2.84 × 1024 to 3.77 × 1024 m−3, and 3.87 × 10−18 to 69.7 × 10−18 m2V−1s−1, respectively for various thicknesses of PPMA thin films. For the higher temperature and lower temperature areas, the activation energies were found in the range from 0.60 to 0.84 eV and 0.28 to 0.40 eV, respectively for 5 V in Ohmic region and from 0.61 to 0.98 eV and 0.27 to 0.34 eV, respectively for 60 V in SCLC (Non-Ohmic) region, respectively. It is observed that SCLC mechanism in PPMA thin films is dominated by a single dominant trap level/discrete trap level distribution. The PPMA thin films are promising candidates in manufacturing optoelectronic devices.

Effect of Trap Behavior on the Reliability Instability of Metamorphic Buffer in InAlAs/InGaAs MHEMT on GaAs.

Our investigation focused on assessing the influence of the metamorphic buffer in metamorphic high-electron-mobility transistors (MHEMT) that were grown on GaAs substrates. While an MHEMT exhibited elevated off-state current levels, its direct current (DC) and radio frequency (RF) traits were found to be comparable to those of InP-based lattice-matched high-electron-mobility transistors (LM-HEMTs). However, the Pulsed I-V measurement results confirmed the presence of the fast transient charging effect, leading to a more substantial degradation in drain current observed in MHEMT. In addition, through the low-frequency noise characteristics, it was confirmed that the dominant trapping location was located in the bulk site. The slope of the 1/f noise measurement indicated that the primary trapping site was in proximity to the bulk traps. The carrier-number-fluctuation (CNF) model was employed to extract the bulk trap density (Nt). For the LM-HEMTs, the value was at 3.27 × 1016 eV-1·cm-3, while for the MHEMT, it was 3.56 × 1017 eV-1·cm-3.

Unintentional p-type conductivity in intrinsic Ge-rich SiGe/Ge heterostructures grown on Si(001)

In this work, we investigate the effective background charge density in intrinsic Si0.06Ge0.94/Ge plastically relaxed heterostructures deposited on Si(001). Hall effect measurements and capacitance–voltage profiling reveal a p-type conductivity in the nominally intrinsic layer with a hole concentration in the mid 1015 cm−3 range at temperatures between 50 and 200 K. In view of the carrier freeze out that we observe below 50 K, we attribute the origin of these carriers to the ionization of shallow acceptor-like defect states above the valence band. In addition, one dominant hole trap located at mid-gap position is found by deep level transient spectroscopy. Carrier trapping kinetics measurements can be interpreted as due to a combination of point defects, likely trapped in the strain field of extended defects, i.e., the threading dislocation.

Integrated Modelling and Reservoir Characterization of Ataga Field, Niger Delta Basin, Nigeria

Integrated modelling, well correlation and petrophysical analysis were performed to characterize the reservoirs for optimum hydrocarbon correlation using 3-D seismic reflection data and suites of well logs from Ataga 5, 7, 10 and 11 wells respectively in Ataga field, shallow offshore, Niger Delta Basin, Nigeria. The study revealed the presence of two viable hydrocarbon bearing reservoirs, AT1 and AT2 and the average values of porosity, permeability, water saturation, hydrocarbon saturation, Net to Gross (NTG) and volume of shale are in the ranges of 15% - 77%, 44.5% - 75.5%, 25.5% - 85%, 15% - 75.5%, 0.70 - 0.88 and 0.11 - 0.38 respectively which goes further to show that the both reservoirs have fair characteristics that are suggestive of the presence of hydrocarbon accumulation. It can therefore be deduced that the permeability values are reflective of fair interconnectivity of pore spaces of sands within the well areas and their ability to transmit fluids, the depth and depth structural map generated for the horizons and structures shows that the most dominant trapping mechanism in the area under study is the crescentic growth fault and the rollover anticlines trending in the Northwest-Southeast direction and from the volumetric analysis. It can be deduced that the recoverable gas for AT1 and AT2 reservoirs is 2 × 106 mscf and 6 × 106 mscf respectively.

Doped low-density parity-check codes

In this paper, we propose a doping approach to lower the error floor of Low-Density Parity-Check (LDPC) codes. The doping component is a short block code in which the information bits are selected from the coded bits of the dominant trapping sets of the LDPC code. Accordingly, an algorithm for selecting the information bits of the short code is proposed, and a specific two-stage decoding algorithm is presented. Simulation results demonstrate that the proposed doped LDPC code achieves up to 2.0 ​dB gain compared with the original LDPC code at a frame error rate of 10−6. Furthermore, the proposed design can lower the error floor of original LDPC codes.

Global sensitivity analysis of CO2 storage in fractured aquifers via computer experiments

• Accelerated CO 2 storage sensitivity analysis via Computer Experiments as surrogate modes. • Rigorous dynamic models use to model non-reactive CO 2 storage mechanisms, inspired by the Teapot Dome in Wyoming dataset. • Demonstration that a network of connected fractures in an eolian sandstone shifts the importance of CO 2 storage controlling parameters. In this work, we use the “Design and Analysis of Computer Experiments” (DACE) technique to analyze the sensitivity of CO 2 storage in fractured aquifers. The aquifer static or geogical model was inspired by the Tensleep formation at Teapot Dome, a potential CO 2 storage target in Wyoming. The CO 2 storage performance in aquifers is comprehensively simulated in our dynamic model by considering all the trapping mechanisms, except for mineralization, i.e. structural, dissolution and residual, as well as local capillary trapping. Operational strategies are investigated to achieve an effective trade-off between higher CO 2 trapping efficiency and delayed CO 2 breakthrough at producers. The effect of natural fractures is explored by running single-porosity, dual-permeability and dual-porosity models. Results show that different models produce significantly different trapping efficiencies, which indicates that natural fractures and their type impact the CO 2 storage practice appreciably. To carry out the global sensitivity analysis, two 100-point computer experiments were designed using the modified space-filling method considering a bottom aquifer, matrix permeability and porosity, fracture permeability and spacing, and water Total Dissolved Solids (TDS). Results show that an active bottom aquifer reduces trapping efficiency noticeably. In addition, dissolution trapping becomes the dominant trapping mechanism. The variability of CO 2 trapping efficiency is explained primarily by fracture permeability, then depth, and finally matrix permeability. In contrast, in the absence of aquifer drive, the variability is almost completely explained by matrix permeability. Furthermore, our results provide guidance to the collection of information as to reduce the most dominant uncertainties.

Optimal turbulent transport in microswimmer suspensions

Microswimmer suspensions self-organize into complex spatio-temporal flow patterns, including vortex lattices and mesoscale turbulence. Here we explore the consequences for the motion of passive tracers, based on a continuum model for the microswimmer velocity field. We observe two qualitatively different regimes distinguished via the dimensionless Kubo number $K$. At advection strengths right above the transition to turbulence, the flow field evolves very slowly ($K \gg 1$) and the spatial vortex structures lead to dominant trapping effects. In contrast, deep in the turbulent state, much faster dynamics ($K \ll 1$) consistent with the so-called sweeping hypothesis leads to transport properties completely determined by the temporal correlations. In between ($K \approx 1$), we observe a regime of optimal transport, signaled by a maximum of the diffusion coefficient.

Interaction of primary precipitates in reduced -activation ferritic/martensitic steel F82H with hydrogen atoms: Atomistic calculation based on the density functional theory

• We used DFT to perform first-principles calculations to understand the fundamental aspects of the interactions between hydrogen isotopes and VC and Cr 23 C 6 crystals in F82H steel. • The single H atom in the carbon vacancy in VC crystal is situated at the center of the vacancy, and the trapping energy is 1.99 eV. • Each H atom and C atom are bound to each other with strong covalent forces, and up to six H atoms can be trapped in the vanadium vacancy in VC crystal. • The trapping energy of H atom in the Cr(8c) vacancy is the strongest among the five types of vacancies in Cr 23 C 6 crystal. To understand the interaction of hydrogen isotopes with VC and Cr 23 C 6 precipitates, in reduced-activation ferritic/martensitic steel (F82H), we have performed first-principles calculations based on density functional theory. Energy calculations and electron density analysis were performed with a focus on the hydrogen retention by vacancies in precipitates. The H atoms in the C vacancy in the VC crystal are bound to the surrounding Cr atoms by relatively weak covalent forces and Coulombic attraction, and up to four H atoms are trapped. In the case of a Cr vacancy, H atoms are strongly covalently bonded to neighboring C atoms as well as to an interstitial H atom, capturing up to six H atoms. H atoms in vacancies in Cr 23 C 6 have a weak bonding force with the Cr atom but a strong repulsive force with the C atom. As a result, H atom is not trapped in the Cr(4a) vacancy, and H atoms are trapped only at a distance from the C atom in the Cr(48H) and Cr(32f) vacancies. The Cr(8c) and C vacancies are relatively far from the C atoms and have higher hydrogen trapping energies. The Cr 23 C 6 precipitate containing vacancies may be a dominant trapping site in the temperature range when H atoms immediately dissociate from vacancies. In addition, the VC precipitate may be the only trapping site for hydrogen isotopes at higher temperatures when Cr 23 C 6 precipitates cannot trap them.

Effective identification of dominant fully absorbing sets for Raptor‐like LDPC codes

AbstractThe error‐rate floor of low‐density parity‐check (LDPC) codes is attributed to the trapping sets of their Tanner graphs. Among them, fully absorbing sets dominantly affect the error‐rate performance, especially for short blocklengths. Efficient methods to identify the dominant trapping sets of LDPC codes were thoroughly researched as exhaustively searching them is NP‐hard. However, the existing methods are ineffective for Raptor‐like LDPC codes, which have many types of trapping sets. An effective method to identify dominant fully absorbing sets of Raptor‐like LDPC codes is proposed. The search space of the proposed algorithm is optimized into the Tanner subgraphs of the codes to afford time‐efficiency and search‐effectiveness. For 5G New Radio (NR) base graph (BG) 2 LDPC codes for short blocklengths, the proposed algorithm finds more dominant fully absorbing sets within one seventh of the computation time of the existing search algorithm, and its search‐effectiveness is verified using importance sampling. The proposed method is also applied to 5G NR BG1 LDPC code and Advanced Television Systems Committee 3.0 type A LDPC code for large blocklengths.

RTS noise in semiconductor devices: time constants estimates and observation window analysis

We obtained a semi-analytical treatment considering estimators for the variance and variance of variance for the RTS noise as a function of the time observation. Our method also suggests a way to experimentally determine the constants of capture and emission in the case of a dominant trap and universal behaviors for the superposition from many traps. We present detailed closed-form expressions corroborated by MC simulations. We are sure to have an important tool to guide developers in building and analyzing low-frequency noise in semiconductor devices.

Effects of Hydrogeological Heterogeneity on CO2 Migration and Mineral Trapping: 3D Reactive Transport Modeling of Geological CO2 Storage in the Mt. Simon Sandstone, Indiana, USA

We used three-dimensional (3D), high-resolution simulations facilitated by parallel computation to assess the effect of hydrogeological heterogeneity in the Mt. Simon Sandstone on CO2 plume evolution and storage and geochemical reactions in a portion of the Illinois Basin, Indiana. Two scenarios were selected to investigate the effects of the hydrogeological heterogeneity in 3D reactive transport simulations: a heterogeneous case with variable porosity and permeability, and a homogenous case with constant porosity and permeability. The initial pressure, temperature, and mineralogical distributions are consistently applied in both the heterogeneous case and the homogeneous case. Results indicate that including hydrogeological heterogeneity in 3D reservoir simulations for geological CO2 storage significantly impacts modeling results for plume migration patterns, CO2-water-mineral interaction, reservoir quality, and CO2 plume containment. In particular, results indicate that (1) the CO2 plume reached the top of the Mt. Simon Sandstone in the homogeneous case, but was restrained to the lower third of the formation when hydrogeologic heterogeneity was considered; (2) the dominant trapping mechanism in the heterogeneous case was mineral trapping (43%), while it was solubility trapping (47%) in the homogeneous case (at 10,000 years); (3) incorporating reservoir heterogeneity in the model leads to a higher likelihood of long-term containment.

Cx43 Promotes Endothelial Cell Migration and Angiogenesis via the Tyrosine Phosphatase SHP-2

The gap junction protein connexin 43 (Cx43) is associated with increased cell migration and to related changes of the actin cytoskeleton, which is mediated via its C-terminal cytoplasmic tail and is independent of its channel function. Cx43 has been shown to possess an angiogenic potential, however, the role of Cx43 in endothelial cell migration has not yet been investigated. Here, we found that the knock-down of Cx43 by siRNA in human microvascular endothelial cells (HMEC) reduces migration, as assessed by a wound assay in vitro and impaired aortic vessel sprouting ex vivo. Immunoprecipitation of Cx43 revealed an interaction with the tyrosine phosphatase SHP-2, which enhanced its phosphatase activity, as observed in Cx43 expressing HeLa cells compared to cells treated with an empty vector. Interestingly, the expression of a dominant negative substrate trapping mutant SHP-2 (CS) in HMEC, via lentiviral transduction, also impaired endothelial migration to a similar extent as Cx43 siRNA compared to SHP-2 WT. Moreover, the reduction in endothelial migration upon Cx43 siRNA could not be rescued by the introduction of a constitutively active SHP-2 construct (EA). Our data demonstrate that Cx43 and SHP-2 mediate endothelial cell migration, revealing a novel interaction between Cx43 and SHP-2, which is essential for this process.

Permeation and trapping of hydrogen in Eurofer97

Diffusion and trapping of hydrogen isotopes in fusion materials need to be fully described in order to evaluate permeation and retention in fusion reactors walls and breeding blankets. Hydrogen gas permeation experiments have been conducted on Eurofer97 with pressures ranging from 1 0 1 to 1 0 5 Pa and temperatures between 473 K and 673 K, resulting in solubility K (T) (mol m −3 Pa − 1 2 )= 1 . 76 ⋅ 1 0 − 1 exp ( − 0 . 27 ( eV ) k B T ) , diffusivity D (T) (m 2 s −1 ) = 2 . 52 ⋅ 1 0 − 7 exp ( − 0 . 16 ( eV ) k B T ) and permeability Φ (T) (mol m −1 Pa − 1 2 s −1 ) = 4 . 43 ⋅ 1 0 − 8 exp ( − 0 . 43 ( eV ) k B T ) . Trapping parameters have been investigated using thermal desorption spectrometry of deuterium-loaded samples coupled with parametric optimization, leading to detrapping energies E dt,1 = 0 . 51 eV , E dt,2 = 1 . 27 eV , E dt,3 = 1 . 65 eV and densities N t , 1 = 6 . 01 ⋅ 1 0 25 m −3 , N t , 2 = 6 . 44 ⋅ 1 0 22 m −3 , N t , 3 = 3 . 88 ⋅ 1 0 23 m −3 . This parametric optimization is performed using a kinetic surface model: the contribution of this model is compared to the results given by solubility and recombination rate models. • Gas permeation yields diffusivity, permeability and solubility of H in Eurofer97. • Effective diffusivity gives the density and energy of the dominant trap. • Thermal desorption spectrometry up to 873K shows three trapping sites. • Using MHIMS, we get energies and densities of the three traps and surface energies.

Analysis of semi-insulating carbon-doped GaN layers using deep-level transient spectroscopy

Electrically active defects in carbon-doped GaN layers were studied with a metal/carbon-doped GaN (GaN:C)/Si-doped GaN (GaN:Si) MIS structure. The GaN:C layers were grown with three different carbon doping concentrations (NC). A semi-vertical metal/semi-insulator/n-type semiconductor (MIS) device was fabricated to perform deep-level transient spectroscopy (DLTS) measurements. Two electron traps E1 and E2 with energy level at EC − (0.22–0.31) eV and EC − (0.45–0.49) eV were observed. E1 and E2 are associated with a nitrogen vacancy VN-related defect in the strain field of extended defects and a nitrogen antisite defect, respectively. By changing the reverse bias voltage of the DLTS measurement, the location and relative defect concentration of the E1 and E2 traps could be verified. A dominant electron trap E3 with an unusual capture cross section was only observed in devices with an NC = 2 × 1019 cm−3 GaN:C layer. This may charge carriers from a defect band and lead to the charge redistribution in the GaN:C layer when forward biased. A hole trap H1 with energy level at EV + 0.47 eV was found for the pulse bias in the forward ON-state. H1 is suggested to correspond with the CN induced 0/+ donor level. By analyzing the schematic band diagrams across the MIS structure, the carrier transport and defect charging mechanisms underlying the DLTS transient measurements are illustrated. The identification of the trap states in the carbon-doped GaN with different NC gives further understanding on the carbon doping impact on electric characteristics of GaN power devices made on Si substrates.

New Structural Percolation Transition in Fractional Wet 3D‐Porous Media: A Comparative μ‐CT Study

AbstractNatural porous media possess spatial heterogeneous (fractional) wettability, which controls the multiphase flow behavior, that is, displacement and trapping. We used mixed hydrophilic (contact angle θ = 0°) and hydrophobic (θ = 100°) 1 mm sands and 1 mm glass beads as model systems for fractional wet porous media. Both porous media have the same morphological characteristics (Minkowski functions). A comparative μ‐CT study of such fractional wet systems is lacking in the literature. A previous study (Geistlinger & Zulfiqar, 2020, https://doi.org/10.1029/2019wr026826) showed a percolation transition of the invading fluid from compact to fractal displacement when the wettability changed from imbibition to drainage. This correlates to a transition from no to maximal trapping. For the first time, we observed in fractional wet glass bead packs, a second structural percolation transition with a percolation threshold of approximately 50% hydrophobic glass beads. Below this threshold, the percolating cluster consisted of hydrophilic glass beads, which resulted in compact displacement without any trapping. Above the threshold, the percolating cluster consisted of hydrophobic glass beads, which resulted in fractal displacement with maximal trapping. Trapping occurred only in hydrophobic environments/configurations, that is, when the trapped clusters were surrounded by hydrophobic glass beads. Fractional wet glass beads and sands show an opposite trapping behavior, that is, the trapping efficiency increases for glass beads, whereas it decreases for sands with increasing percentage of hydrophobic grains. Interestingly, the trapping efficiency approaches the same limit value for pure hydrophobic sands and glass beads. This demonstrates that bypass trapping is the dominant trapping mechanism, because it depends strongly on the pore connectivity.

Identification of lead vacancy defects in lead halide perovskites

Perovskite photovoltaics advance rapidly, but questions remain regarding point defects: while experiments have detected the presence of electrically active defects no experimentally confirmed microscopic identifications have been reported. Here we identify lead monovacancy (VPb) defects in MAPbI3 (MA = CH3NH3+) using positron annihilation lifetime spectroscopy with the aid of density functional theory. Experiments on thin film and single crystal samples all exhibited dominant positron trapping to lead vacancy defects, and a minimum defect density of ~3 × 1015 cm−3 was determined. There was also evidence of trapping at the vacancy complex ({{{{{rm{V}}}}}}_{{{{{rm{Pb}}}}}}{{{{{rm{V}}}}}}_{{{{{rm{I}}}}}})^{-} in a minority of samples, but no trapping to MA-ion vacancies was observed. Our experimental results support the predictions of other first-principles studies that deep level, hole trapping, {{{{{{rm{V}}}}}}}_{{{{{{rm{Pb}}}}}}}^{2-}, point defects are one of the most stable defects in MAPbI3. This direct detection and identification of a deep level native defect in a halide perovskite, at technologically relevant concentrations, will enable further investigation of defect driven mechanisms.

Deep-Level Traps Responsible for Persistent Photocurrent in Pulsed-Laser-Deposited β-Ga2O3 Thin Films

Gallium oxide (β-Ga2O3) is emerging as a promising wide-bandgap semiconductor for optoelectronic and high-power electronic devices. In this study, deep-level defects were investigated in pulsed-laser-deposited epitaxial films of β-Ga2O3. A deep ultraviolet photodetector (DUV) fabricated on β-Ga2O3 film showed a slow decay time of 1.58 s after switching off 250 nm wavelength illumination. Generally, β-Ga2O3 possesses various intentional and unintentional trap levels. Herein, these traps were investigated using the fractional emptying thermally stimulated current (TSC) method in the temperature range of 85 to 473 K. Broad peaks in the net TSC curve were observed and further resolved to identify the characteristic peak temperature of individual traps using the fractional emptying method. Several deep-level traps having activation energies in the range of 0.16 to 1.03 eV were identified. Among them, the trap with activation energy of 1.03 eV was found to be the most dominant trap level and it was possibly responsible for the persistent photocurrent in PLD-grown β-Ga2O3 thin films. The findings of this current work could pave the way for fabrication of high-performance DUV photodetectors.